Before creating a new topic, please search the Community to avoid creating duplicate threads. If you are posting about a problem, the more of the below details you can include (if applicable) the easier it will be for others to try and help. Go to https://bose.life/2K1GbJl for a helpful post on how to find relevant information, including your firmware and app version information!
Bose product name
What devices were you using that were affected and what version are they on (e.g. Samsung Galaxy S9 on Android 11, iPhone X on iOS14, etc.)
Detailed description of the issue and steps to reproduce
What environment do you experience the issue in? (e.g. noisy office, quiet kitchen, etc.)
When did you start to experience the issue? Did it work correctly previously?
Are you referring to the plastic or the ear cushions? For the later, you can, for example go to eBay or Amazon and do a search on the name of your Bose product (like QC35, QC25, or QC15) and 'ear cushion'. You'll probably get many many matches.
If you are referring to the plastic that you have highlighted in yellow, it is not a part and can not be replaced. If that is an issue for you, you need to call Bose and arrange for an exchange - they do not repair. You may need to pay unless it is under warranty and is a defect or normal wear and tear.